Wild monkeys in the Fukushima region of Japan have blood abnormalities linked to the radioactive fallout from the 2011 nuclear power plant disaster, according to a new scientific study that may help increase the understanding of radiation on human health.

The Japanese macaques (Macaca fuscata) were found to have low white and red blood cell levels and low haemoglobin, which the researchers say could make them more prone to infectious diseases.

But critics of the study say the link between the abnormal blood tests and the radiation exposure of the monkeys remains unproven and that the radiation doses may have been too small to cause the effect.

The scientists compared 61 monkeys living 70km (44 miles) from the the Fukushima Daiichi nuclear power plant with 31 monkeys from the Shimokita Penisula, over 400km (249 miles) from Fukushima. The Fukushima monkeys had low blood counts and radioactive caesium in their bodies, related to caesium levels in the soils where they lived. No caesium was detected in the Shimokita troop.

Professor Shin-ichi Hayama, at the Nippon Veterinary and Life Science University in Tokyo, told the Guardian that during Japan’s snowy winters the monkeys feed on tree buds and bark, where caesium has been shown to accumulate at high concentrations.

“This first data from non-human primates — the closest taxonomic relatives of humans — should make a notable contribution to future research on the health effects of radiation exposure in humans,” he said. The work, which ruled out disease or malnutrition as a cause of the low blood counts, is published in the peer-reviewed journal Scientific Reports.

White blood cell counts were lowest for immature monkeys with the highest caesium concentrations, suggesting younger monkeys may be more vulnerable to radioactive contamination. Hayama noted: “Abnormalities such as a decreased blood cell count in people living in contaminated areas have been reported from Chernobyl as a long-term effect of low-dose radiation exposure.” But other blood measures did not correlate with caesium levels, which vary with the seasons.

Prof Geraldine Thomas, at Imperial College London, said the Chernobyl studies were not “not regarded as scientifically validated” and that the correlations between the caesium and low blood counts in the Fukushima study were not statistically strong.

“Unfortunately, this is yet another paper with insufficient power to distinguish real effects and relevance to human health,” she said. “We know that one of the most damaging health effects comes from fear of radiation, not radiation itself.” She also noted that people, unlike the monkeys, could avoid eating contaminated food from the Fukushima region.

Another critic, Prof Jim Smith, at the University of Portsmouth, said: “I am highly sceptical of the claim. The levels of radiocaesium in the Fukushima monkeys are about the same as those found in sheep in some parts of the UK following the Chernobyl accident, i.e., extremely low in terms of damage to the animals themselves. I think it much more likely that the apparently low blood cell counts are caused by something other than radiation.”

Prof Hayama said that caesium levels were used as an indicator of the radiation exposure of the monkeys. “The low haematological values in the Fukushima monkeys could have therefore been due to the effect of any radioactive materials,” he said. “We did not conclude the low-blood cell counts are caused by caesium but so far we cannot find other reasons except radiation.”